Biodegradable microparticles may be used to deliver drugs, hormones, proteins, and other medically active agents to a patient. As they degrade, the microparticles may gradually release agents to the body intravenously or subcutaneously and may be administered to the body with a needle. Biodegradable microparticles may reduce the frequency of injections, as the agents are released gradually into the body. The microparticle size distribution and flowability characteristics affect the gauge and other characteristics of the needle. More flowable microparticles may be easier to fill into vials and may be more easily injected with a large gauge (smaller diameter) needle. Once in the body, the rate of release and the concentration of the medically active agent may be related to the microparticle size, the microparticle size distribution, the initial concentration of the medically active agent, and other characteristics of the microparticles. Such biodegradable microparticles also need to meet health and safety regulations for contaminant concentrations including the solvents used to prepare the microparticles. Thus, a need for microparticles with superior syringability, injectability, flowability, uniformity, and purity characteristics exists. The methods and systems described herein provide solutions to these and other needs.